When a volume within a storage subsystem runs out of space, the host using the volume will need additional storage to continue I/O operations. The conventional method of manually configuring storage space by creating and assigning a new volume to the host or increasing the capacity of an existing volume is time consuming and risks causing significant downtime.
Aside from manual configuration, another technique sometimes used is called thin provisioning. With thin provisioning, a user can create a volume specifying a size but physical storage is only allocated to the volume as data is written. However, once the allocated capacity reaches the originally requested capacity for the volume, no more data can be written to the volume until it is re-sized, thus resulting in the need to manually add capacity to the volume.